The invention relates to an electric load comprising a carrier plate of an insulating material,
at a first side of which, there are contacts and means for mechanically coupling the load to a holder, and
at a second side of which, there is a load element,
which load element has current conductors, which are connected to a respective contact.
Such an electric load is disclosed, for example, in U.S. Pat. No. 3,780,327.
The known load is a glow switch, which can be used to ignite low-pressure mercury vapor lamps, such as fluorescent lamps. The contacts of said glow switch are brass pins having a first constriction between their free end and the plate. In commercially available glow switches, the carrier plate is made of hard paper, and the pins have a second constriction which is inserted in an opening in the carrier plate, so that the first constriction forms a stop at the first side of the plate. From the second end, t he pins are provided with a bore wherein the relevant current conductor is fixed. Said second end is curled over so as to fix the pin in the carrier plate.
In the known load, the contacts also serve as the means for mechanically coupling the load to a holder. For this purpose, the holder has a wall with arc-shaped slots having a circular opening at one end. When the load is placed in the holder, the free ends of the contacts are passed through a respective opening and the load is turned, causing the first constriction to move through a relevant slot towards an end position. As a result, the load is mechanically coupled to the holder. In addition, the free ends of the contacts make lateral, electric contact with the holder.
A drawback of the known electric load resides in that the contacts have a comparatively large material content. Another drawback resides in that the contacts are difficult to manufacture. These drawbacks result in a comparatively high cost price of the contacts and hence the load.
It is an object of the invention to provide an electric load of the type described in the opening paragraph, the construction of which is simple and readily manufacturable at comparatively low costs.
In accordance with the invention, this object is achieved in that
the carrier plate comprises synthetic resin projections, which serve as means for coupling the load to a holder,
which projections are provided with a shank with a disc at some distance from the carrier plate, which projections are further provided with a duct accommodating one of the current conductors,
which disc has an end face facing away from the carrier plate and a circumferential side face,
at least the side face being covered with an electric conductor, which is connected as a contact to the relevant current conductor.
In the load in accordance with the invention, comparatively large brass parts are replaced with synthetic resin projections. The synthetic resin projections serve as means for coupling the load to a holder, and they are also used as contact carriers. As a result, the contacts are much smaller than the contacts of the known load and have a much smaller material content. Synthetic resin can be readily shaped in a mold, and is a comparatively inexpensive material. It is sufficient to cover the side face, i.e. the face of the projection, with an electric conductor. The side face must actually be electrically connected with the holder.
The projections and the carrier plate can be joined to each other, for example by fusing or bonding, but, advantageously, the projections are integral with the carrier plate. The carrier plate with the projections may be made, for example, from a thermoplast, such as polyamide or polycarbonate.
In a favorable embodiment, also the end face is covered with the electric conductor. As a result, the projection may have a wholly axially extending duct for accommodating a current conductor, which can be connected at the end face to the electric conductor. By virtue thereof, the projections, or the carrier plate including the projections, can be manufactured even more readily. The end face may be provided with a recess around the duct, in which recess the current conductor is connected to the electric conductor, so that the connection is recessed. The connection may be formed, for example, using solder or by means of drop-deposition of a metal.
The electric conductor may be a coating, for example of a metal. It is favorable, however, if the electric conductor is a metal body, for example of brass, which is secured to the projection. In the latter case, the body is, for example, a cylindrical body which is open on two sides or a cylindrical body having a bottom portion, which bottom portion covers the end face of the projection. The body may be fixed in position by curling it around the disc of the relevant projection. The body may alternatively be in tight working contact with the projection, for example through a press fit. In this case, the current conductor, which is bent back around the disc, may also be tightly fitted. Alternatively, the carrier plate with the projections may be formed in a mold in the presence of the metal bodies. This method of manufacturing is referred to as xe2x80x9cinsertion moldingxe2x80x9d.
In a favorable embodiment, the electric conductor is a cylindrical body having a bottom portion and a tubular portion extending in the body of the bottom portion, which tubular portion is accommodated in the duct of the projection. This embodiment has the advantage that the current conductor and the electric conductor co-operate telescopically. This enables the load element to be readily positioned at a predetermined distance from the carrier plate, whereafter the current conductors are connected to the electric conductor by means of, for example, solder. In addition, this embodiment has the advantage that the carrier is provided with the means for coupling to a holder, and with the contacts, prior to being united with the load element.
In a modification, the shank of the projection has a radial bore which opens into the duct, and the tubular portion is indented via the bore so as to keep the current conductor in a fixed position. This modification has the advantage that only one mechanical operation has to be carried out to make a connection between the current conductor and the electric conductor.
The metal body present at the projections can be easily manufactured in an accurate and comparatively cheap manner by machining, for example, brass, in which operation the material is upset and formed.
The electric load may be, for example, an electric lamp, such as a LED or an incandescent lamp, in which case the load element comprises a light-emitting diode or an incandescent body, respectively. The electric load may alternatively be a switch, for example a glow switch, which is used, for example, to ignite a low-pressure mercury vapor lamp, such as a fluorescent lamp. In this case, the load element may comprise, for example, an electrode and a bimetal electrode in an envelope filled with an inert gas, which may be bridged (?) by an anti-interference capacitor. The load element may be accommodated in a, for example synthetic resin, housing which is attached to the carrier.